(1) Field of the Invention
The present invention relates to the fabrication of micro electro-mechanical devices, and more particularly, to a method of eliminating nitride residue between mirrors for a reflective spatial light modulator in the fabrication of micro electro-mechanical devices.
(2) Description of the Prior Art
A double substrate spatial light modulator includes mirrors suspended by hinges from an upper substrate. Individual mirrors can be selectively deflected to spatially modulate light incident to the upper substrate and then to reflect the light back to the upper substrate. The mirror twist angle can be controlled by changing the input voltage of the high voltage (HV) devices. The mirror twist angle effects the light reflection path. Therefore, different reflection paths can be treated as On/Off states.
FIG. 1 illustrates a double substrate spatial light modulator. Micromirrors 16 are attached to a glass substrate 10 by hinges 20. Electrodes 44 on a CMOS substrate 40 control the deflection of the mirrors. CMOS HV devices are formed within the substrate 40. Light is reflected as shown by 45 and 47. Mirrors 16 are illustrated in another view in FIG. 2. In making the mirrors, silicon nitride residue can prevent free movement of the mirrors. It is desired to provide a process for fabricating micromirrors wherein the silicon nitride residue problem is eliminated.
U.S. Pat. No. 6,337,760 to Huibers et al, U.S. Pat. No. 6,046,840 to Huibers, U.S. Pat. No. 6,356,378 to Huibers, U.S. Pat. No. 6,275,325 B1 to Sinclair, and U.S. Pat. No. 6,396,619 B1 to Huibers et al show mirrors with different types of hinges. U.S. Pat. No. 6,329,738 B1 to Hung et al shows a mirror with no hinge.